Aluminum is one of the three primary materials used today in semiconductor structures, the other two being silicon and silicon dioxide. It is primarily used in thin films as an interconnect between the specific structures formed on semiconductor substrates or substrate assemblies. Aluminum has been an important material in the fabrication of semiconductor structures because of its high conductivity, low resistivity (2.7 μΩ-cm), high adherence to silicon and silicon dioxide, and low stress. Its use is also expanding into other metallization applications. For example, it is being examined to replace tungsten in contacts or vias (i.e., very small openings located, for example, between surface conductive paths and or “wiring” and active devices on underlying layers), which are getting narrower and deeper, and harder to fill with metal.
Aluminum alloys are also used in semiconductor structures, including alloys of aluminum with copper, titanium, etc., and combinations thereof. The addition of small quantities (typically, about 0.1–4%) of other metals to aluminum improves the electromigration resistance and reduces the propensity of aluminum thin-films to form hillocks (i.e., protrusions on the aluminum film surface). Such films, however, have increased resistivity over that of pure aluminum films.
In some applications, aluminum films are deposited using sputtering techniques; however, sputtered aluminum is not effective at filling contacts or vias because of shoulders or overhangs that form at the contact openings. These overhangs can lead to the formation of keyhole-shaped voids. Various collimation techniques help reduce this problem, but typically not enough to enable complete filling of very small geometries (e.g., less than about 0.5 μm). Therefore, it is desirable to use chemical vapor deposition (CVD) to form aluminum and aluminum alloy films.
Dimethylaluminum hydride has emerged as one of the preferred materials for aluminum metallization by CVD. A serious problem with this material, however, is its pyrophoricity. This problem has been addressed to some degree by the addition of amines to the compound to act as stabilizing Lewis base donors to the aluminum center. However, such precursor compounds are still pyrophoric, albeit to a lesser extent. An additional complicating factor is introduced into the vapor pressure behavior of the precursor as a result of dissociation of the amine. Thus, there is a continuing need for methods and precursors for the deposition of aluminum and aluminum alloy films, as well as other Group IIIA metal or metal alloy films, on semiconductor structures, particularly using vapor deposition processes.